Electric translating system



Feb. 18, 1958 w. J. HOLT, JR 2,824,274

ELECTRIC TRANSLATING SYSTEM Filed Deo. 15, 1952 2 sheets-sheet 1 Feb.18', 1958 w. J. HoLT, JR 2,824,274

ELECTRIC TRANSLATING SYSTEM Filed Dec. 15, 1952 2 Sheets-Sheet 2 .7N VENTOR.

WILLA J. HOLT JR: BW

United States Patent Oflice 2,824,274 Patented Feb. 18, 1958 ELECTRICTRANSLATING SYSTEM William J. Holt, Jr., Garland, Tex., assigner to VaroMfg. Co., Inc., Garland, Tex.

Application December 1S, 1952, Serial No. 326,009. 11 Claims. (Cl.321-27) This invention relates to electric translating systems and moreparticularly to electric translating systems for transmitting energyfrom a direct current supply circuit to an alternating current loadcircuit.

Electric translating apparatuses of the parallel inverter type disclosedin my co-pending application, Serial --mber MWI/33, tiled luly 3S, 1949,i ateut Number j 569, issued May l2, i953, can transmit only limitedamounts of energy from a direct current supply circuit to au alternatingcurrent load circuit due to the current carrying limita lons of thevarious components of such apparatuses and especially ot the gaseousdischarge valves which are connected in parallel across the directcurrent supply circuit. ln certain installations which require thetransmittal of large amounts ot energy between the direct current supplycircuit and me alternating current load circuit, it is desirable toconnect a plurality of such apparatuses in parallel between the supplyand load circuits. lt is necessary that the alternating current outputsof such parallel connected apparatuses be in phase with one another andthat each of the apparatuses transmit a predetermined proportion of thetotal energy supplied to the load circuit regardless of fluctuation inthe voltage of the supply circuit. lt is desirable therefore to providean electric translating system for transmitting large amounts of energyfrom a direct current supply circuit to an alternating current loadcircuit which comprises a plurality of inverters each of which transmitsa predeteriined proportion of the total energy supplied to the loadcircuit.

Accordingly, it is an object of the invention to provide a new andimproved electric translating system for transmitting energy from adirect current supply circuit to an alternating current load circuit.

lt is another object of the invention to provide a new and improvedelectric translating system for transmitting large amounts of currentfrom a direct current supply circuit to an alternating current loadcircuit.

it is still another object of the invention to provide a new andimproved electric translating system having a plurality of parallel typeinverters connected in parallel between a direct current supply circuitand an alternating current load circuit.

lt is a further object of the invention to provide a new and improvedelectric translating system having a plurality of parallel typeinverters connected in parallel between a direct current supply circuitand an alternating current load circuit and having control means forpredetermining the proportion of the total energy supplied to the loadcircuit by each of the inverters.

lt is a still further object of the invention to provide a new andimproved electric translating system having a plurality of invertersconnected in parallel between a direct current supply circuit and asingle phase alternating current load circuit and having control meansfor predetermining the proportion of the total energy supplied to theload circuit by each of the inverters.

lt is another object of the invention to provide a new and improvedelectric translatin7 system having a plurality of inverters connected inparallel between a direct current supply circuit and a three phasealternating current load circuit and having control means forpredetermining the proportion of the total energy supplied to the loadcircuit by each of the inverters.

Briefly stated, the new and improved electric translating systemcomprises a plurality or" inverters of the parallel type connected inparallel between a direct current supply circuit and a single phasealternating current load circuit. One of these inverters may be termedthe master inverter and the others slave inverters. Each of theinverters includes a pair of electric valves connected in parallel whichare rendered alternately conductive by an alternating potentialimpressed on their control grids from an alternating current source ofthe esired frequency. The alternating potentials impressed on thecontrol grids of the electric valves of the inverters are supplied froma common source so that the alternating current outputs of the invertersare in phase. The master inverter is provided with a voltage regulatingmeans which tends to maintain the voltage of the load circuitsubstantially constant. A plurality of current balance sensingtransformers is provided each of which has a secondary winding in whichis induced a voltage which varies in accordance with the difference inthe amount of current supplied to the load circuit by the masterinverter and one of the slave inverters. The secondary winding of eachof the current balance sensing transformers is connected to the voltageresulating means of its associated slave inverter to vary the voltage ofthe output of the slave inverter in accordance with the variations inthe difference in the amounts of current supplied to the load circuit bythe master inverter and the slave inverter to maintain substantiallyconstant the predetermined proportion of the total current supplied toload circuit by each slave inverter.

ln another embodiment of the invention a master inerter and two slaveinverters are connected in parallel between a direct current supply anda three phase alternating current Load circuit. Each of the invertersincludes a pair ot electric valves connected in parallel which arerendered alternately conductive by alternating potentials impressed ontheir control grids from an alternating current source of the desiredfrequency. These alternating potentials are properly displaced in phaseby phase shifting circuits so that the alternating current outputs ofthe inverters differ in phase by electrical degrees from one another.The master inverter is provided with a voltage regulating means whichtends to maintain the voltage of the load circuit substantiallyconstant. Each of the slave inverters is provided with a current balanceor ratio sensing circuit for producing a control voltage or potentialwhich varies in accordance with the balance or ratio between thealternating current output of each inverter and the alternating currentoutput of the master inverter. The control voltages o1 potentials arefed to the voltage regulating means of each of the slave inverters tomaintain substantially constant the predetermined balance or ratio.

For a better understanding of the invention, reference may be had to thefollowing description taken in connection with the accompanying drawingand its scope is pointed out in the appended claims. In the drawing,Figure l illustrates diagrammatically the electric translating systemfor transmitting energy from a direct current supply circuit to a singlephase alternating current load circuit; Figure 2 illustratesdiagrammatically the electric translating system for transmitting energyfrom a direct current supply circuit to a three phase alternatingcurrent load circuit.

Referring now to the drawing, the electric translating system fortransmitting energy from a direct current supply circuit to analternating current load circuit 11 includes a plurality of inverters12, 13, and 14 connected in parallel between the supply and loadcircuits 16 and 11` The inverter 12 may be termed the master inverterand the inverters 13 and 14 may bev termed slave inverters for reasonswhich will be developed below. The master inverter includes atransformer 15 provided with a primary winding 16 having its electricalmidpoint connected to one side of the supply circuit through a smoothingreactor 17 and end terminals connected to the other side of the supplycircuit through electric valves 18 and 19. Electric valves 18 and 19 areeach provided with an anode 20, a cathode 21, and a control grid 22.Commutating capacitor 23 is connected between the anodes 20 of theelectric valves. The electric valves are preferably of the gaseousdischarge type.

In order periodically to render the electric valves 1S and 19alternately conductive and non-conductive, their control grids 22 areconnected to their common cathode circuit through current limitingresistance 24 and opposite halves of the secondary winding 25 of a griddrive transformer 26 whose primary winding 27 is connected to a source28 of alternating current of the desired frequency. The current limitingresistance 24 is connected between the electrical midpoint 29 of thesecondary winding 25 and the cathodes 21 of the electric valves toprovide a high resistance path for current flow from the cathodes 21 tothe control grids 22.

The general principle of operation of the master inverter will be wellunderstood by those skilled in the art. In brief, if one of the electricvalves, for example, the valve 18, is initially rendered conductive,current will flow through the upper portion of the primary winding 16and the electric valve 18, inducing one-half cycle of alternatingcurrent in the secondary windings 36 and 31 of the transformer 15.During this interval, the capacitor 23 becomes charged to substantiallytwice the potential of the direct current supply circuit 10 and when thegrid potential supplied by the secondary winding 25 reverses polarity torender the valve 18 conductive, the potential of capacitor 23 iseffective to commutate the current from the valve 18 to the valve 19.Current then flows through the lower portion of winding 16 inducing ahalf cycle of alternating current of opposite polarity in the secondarywindings and 31. in this manner the current is successively commutatedbetween the valves 18 and 19 and alternating currents are induced in thesecondary windings of the transformer 15.

The voltage induced in secondary winding 30 is maintained substantiallyconstant by means of a saturable reactor 32 whose reactive winding 33 isconnected across the commutating capacitor 23 and whose saturatingwinding 34 is supplied with direct current from a rectier 35 through acontrol electric discharge means 36. The rectier 35 may be an electricdischarge means having a pair of anodes 37 and 38 connected to theopposite ends of the secondary Winding 31 and a cathode 39 connected toone side of the saturating winding. The control electric discharge means36 includes an anode 4t) connected to the other side of the saturatingwinding, a cathode 41 connected to the electrical midpoint 4:2 of thesecondary winding 31, and a control member or grid 43. If the impedanceof the saturable reactor 32 is increased, the voltage across the primarywinding 16 is increased. As a result, the voltage across the secondarywinding 3d) is also increased. Conversely, if the impedance of thesaturable reactor is decreased, the voltage across secondary winding 30is decreased. The impedance of saturable reactor can be controlled byVarying the conductivity of the control electric discharge means 36. Ifthe conductivity of electric discharge means 36 increases with anincrease of the voltage 11, the current flowing in the saturatingwinding 34 is increased and the impedance of saturable reactor 32 isdecreased. This causes a decrease in the voltage induced in thesecondary windings 36 and 31, therefore a decrease in the voltage of thealternating current load circuit. On the other hand, if the conductivityof the control electric discharge means 36 is decreased, the impedanceof the saturable reactor 32 is increased and the voltage of thealternating current load circuit is increased.

The control means for varying the conductivity or" electric dischargemeans 36 in accordance with the voltage of the load circuit includes avoltage sensing transformer 44 having a primary winding .5 connectedacross the Y load circuit. A rectier electric discharge means 46 hasanodes 47 and i3 connected to opposite ends of the secondary winding 49of the voltage sensing transformer and a cathode 5t). A filter which maycomprise a pair of capacitors 51 and 52, and a reactor 53 is provided tosmooth the output of the rectifier electric discharge means 46. A glowdischarge means 54 and a resistance 55 are connected in series acrossthe output terminals 57 and 5S ofthe rectiiier 46 and comprise a voltagedivider bridge. rhree serially connected resistances 59, 66, and 61, arealso connected across the output terminals 57 and 53. An electricdischarge means 62 has an anode 63 connected to the terminal 57 througha resistance 64 and a cathode 65 connected to the other terminal throughresistance 55.

The control grid 66 of the electric discharge means 62 is connected tothe resistance 66 through an adjustable contact 67 in order that apotential be impressed on the control grid 66 which varies a fixedfraction of the varia tions in the voltage across the terminals. Sincethe cathode 65 is connected to the common juncture or connection 63 ofthe glow discharge means 5ft and the re sistance 55, the totalvariations in the voltage across the terminals 57 and 58 will beimpressed on the cathode 65 because the voltage drop across the glowdischarge means 54 will remain constant. The variation in the potentialof the cathode 65 will therefore be the main factor affecting theconductivity of the electric discharge means 62. For example, if thevoltage across the terminals 57 and 53 increases a certain amount, thepotential of the cathode 65 will also become more positive or lessnegative by the same amount. The potential impressed on the control grid66 will also become more positive or less negative but only by afraction of the amount of the change in the voltage across theterminals. in effect, the control grid 66 becomes more negative withrespect to the cathode 65 and the conductivity of the electric dischargemeans 62 is decreased. 1f the voltage across the terminals drops, theconductivity of the electric discharge means 62 is increased. Since thecontrol grid 43 of the control electric discharge means 36 is connectedto the common juncture or connection 69 of the resistance 64 and theanode 63, the conductivity of the control electric discharge means 36will vary indirectly as the conductivity of the electric discharge means62 increases when the conductivity of the electric discharge meansdecreases and vice versa.

It will be apparent now that if the voltage across the load circuit 11increases, the electric discharge means 62 becomes less conductive, thecontrol electric discharge means 36 becomes more conductive and, as aresult, more current ows through the saturating winding 34 of thesaturable reactor 32 decreasing the impedance of the inductive winding33 of the reactor 32. The voltage of the load circuit thereforedecreases. Conversely, if the voltage across the load circuit decreases,the electric discharge means becomes less conductive, and, therefore,less current flows through the saturating winding. The impedance of theinductive winding 33 increases causing the voltage across the loadcircuit to increase. In this manner, the voltage of the load circuit 11is maintained substantially constant,

Either, or both, the commutating capacitor 23 and the saturable reactor32 can be connected across the secondary winding 3d if desired; thecommutating capacitor and the saturable reactor each being capable ofperforming its function regardless of whether it is connected across theprimary winding or the secondary winding of the transformer 15.

The slave inverters 13 and 14 and their control circuits are substantialduplicates of the master inverter and its control circuit and,therefore, in order to avoid prolixity, corresponding elements of theinverters and their control circuits have been provided with the samereference numerals, the letter a being added to the reference numeralsof the corresponding elements of the inverter 13, and the letter b beingadded to the reference numerals of such corresponding elements of theinverter 14.

Since it is desirable that each of the inverters transmit apredetermined proportion of the total energy supplied to the loadcircuit 1l, the current balances between the output of the slaveinverters 13 and 14 and that of the master inverter 12 are sensed by thecurrent balance sensing transformers 70 and 71, respectively. Thetransformer 70 includes a core 72 having outer legs 73 and 74 and acenter leg '75. The winding 76 on the outer leg 73 is connected inseries with the secondary winding 30 so that the alternating currentoutput of the master inverter flows through the winding 76 and induces amagnetic flux in the legs 73 and 75, which tends to induce analternating voltage of one phase in the control winding 77 disposed onthe center leg 75. The Winding 7S on the outer leg 7d is connected inseries with the secondary winding 3de so that the alternating currentoutput of the slave inverter 13 Hows through the winding 7S and inducesa magnetic flux in the legs 74 and 75 which tends to induce analternating voltage of the opposite phase in the control winding 77. Thecontrol winding 77 is connected in series with the winding 45a of thetransformer 44a across the winding 30a so that the voltage induced inthe primary winding 49a is a resultant of the voltage and phase of thealternating voltage in the control Winding 77 and of the alternatingvoltage of the winding 39a. The winding 45a and '77 are connected acrossthe winding 30a in order that a predetermined potential be applied tothe control grid 43a of the control electric discharge means 36a so thatcurrent of a predetermined value ows through the saturating winding 34aof the saturable reactor 32a when no alternating current is induced inthe control winding 77. This condition occurs when the alternatingcurrent outputs of the master inverter 12 and the slave inverter 13 areequal or balanced.

If the output of the slave inverter 13 now increases so that it exceedsthat of the master inverter 12, and alternating voltage is induced inthe control winding 77 which varies as the difference in the outputs andwhich is of the same phase as the alternating voltage induced in thewinding 30a. As a result, the alternating voltage induced in winding 49aincreases, the electric discharge means 36a is rendered more conductiveand transmits more current to the saturating winding 34a, and thevoltage induced in the winding 30a decreases, the alternating currentoutput of the slave inverter thus decreasing until it substantiallyequals the output of the master inverter.

lf the output of the slave inverter now decreases so that it is lessthan that of the master inverter, and alternating voltage is induced inthe control Winding 77 which varies as the difference in the outputs andwhich is of the opposite phase as the alternating voltage induced in thewinding Sila. As a result, the alternating voltage induced in winding49a decreases, the electric discharge means 62a becomes more conductive,the control electric discharge means 36a is rendered less conductive andtransmits less current to the saturating winding 34a and the voltageinduced in the winding 30a increases the alternating current output ofthe slave inverter 13, thus decreasing until it substantially equals theoutput of the master inverter. In this manner, the outputs of the vslaveand master inverters are kept balanced.

It will be noted that the alternating current output of the slaveinverter is varied in accordance with the variations inthe balancebetween the outputs of the master and slave inverters, by varying thevoltage of the alternating current output of the slave inverter. Thevoltage of the output circuit 11 is maintained constant by the voltagecontrol circuit of the master inverter.

The current balance sensing transformer 71 similarly controls the outputvoltage of the slave inverter 14 to maintain constant the currentbalance between the outputs of the master inverter and the slaveinverter. The transformer 71 includes a core 79 having outer legs 80 and81 and a center leg 82. A primary Winding 83 is disposed on the outerleg and is connected in series with the primary winding 76 of thetransformer 70 and the secondary winding 3) of the master inverter sothat an alternating magnetic uX is induced in the outer leg 80 and thecontrol leg 82 of the core which varies in accordance with thealternating current output of the master inverter and tends to induce analternating voltage of one phase or polarity in the secondary winding 84and of the center leg 82. A winding is disposed on the outer leg 81 andis connected in series with the secondary winding 3919 of the slaveinverter 14 so that an alternating magnetic tlux is induced in the outerleg 81 and the control leg 82 which tends to induce an alternatingvoltage of the opposite phase or polarity in the secondary winding 84.The secondary winding 84 is connected in series with the winding 45b ofthe transformer 44h across the winding 30b so that the voltage inducedin the primary winding 49h is a resultant of the voltage and phase ofthe alternating voltage in the secondary winding 84 and of thealternating voltage of the winding 30b.

The output of the slave inverter 14 is controlled in exactly the samemanner as that of the slave inverter 14 in accordance with thevariations in the balance between the alternating current outputs of themaster inverter and of the slave inverter in order to maintain apredetermined balance therebetween.

lt will now be apparent that the master inverter 12 and the slaveinverters 13 and 14 each transmit a predetermined proportion of thetotal energy supplied to the load circuit 1l from the supply circuit1t). It will also be apparent that each of the inverters is capable ofoperating independently to energize a constant voltage alternatingcurrent load circuit when its winding 45, 45a or 45h, as the case maybe, is connected across the load circuit 11, and that these inverterscan be easily connected in parallel between a direct current supply andan alternating current load circuit by connecting the windings of two ofthe inverters, 45a and 45!) in series with suitable secondary windingsof current balance sensing transformers in which are induced controlvoltages which vary in accordance with the variations in the balancesbetween the alternating current outputs of the two inverters and thethird inverter and that the control voltages are employed to vary thevoltage of the alternating current outputs of the two inverters tomaintain substantially constant the balances between the amounts ofcurrent transmitted to the load circuit by each of the two inverters andthe third inverter.

Although in the illustrated and described system, the three inverters,12, 13, and 14, transmit equal amounts of alternating current, it willbe apparent that the balance between the alternating current outputs ofthe master inverters and each of the slave inverters may be set at anypredetermined ratio by varying the ratio of the number of turns in theprimary winding 74 to the number of turns in the primary winding 76, andby varying the ratio of the number of turns in the primary winding $3 tothe number of turns in the primary winding 8S. For example, if thenumber of turns in the primary winding 74 is twice the number of turnsin the primary esagera winding 76, the master inverter 12 will delivertwice as much current to the load circuit as the slave inverter 13.Similarly, by'varying the ratio of the number of turns in the secondarywinding 83 to the number of turns in the secondary winding 85, thebalance between the amounts of current transmitted to the load circuitby the master inverter and the slave inverter 14 may be set at anypredetermined ratio. These variations in the ratios of the Iamounts ofcurrent transmitter by the inverters may be necessary or desirable wherethe inverters are of different capacities and it is desired to utilizeeach inverter at its optimum operating conditions.

Moreover, it will be apparent that any number of slave inverters may beconnected in parallel with the master inverter between the supplycircuit and the load circuit, it being necessary to provide anadditionalcurrent balrance sensing transformer for each additional slave in verteradded. For example, if only one slave inverter is connected in parallelwith the master inverter, only one current balance sensing transformeris needed; if three slave inverters are connected in parallel, threecurrent balance sensing transformers are needed, and

so on.

In Figure 2 is illustrated an electric translating system fortransmitting energy from a direct current supply circuit 101 to apolyphase alternating current load circuit having terminals 102, 103,and 104 which includes a master inverter 105 and slave inverters 106 and107. The master inverter 105 includes a transformer 10S provided with aprimary winding 109 having its electrical midpoint connected to one sideof the supply circuit through a smoothing reactor 110 and end terminalsconnected to the other side of the supply circuit through electricvalves 111 and 112. Electric valves 111 and 112 are each provided withan anode 113, and a cathode 114, and a control grid 115. A commutatingcapacitor 116 is connected across the secondary winding 117 of thetransformer 108. The electric valves are preferably of the gaseousdischarge type.

In order periodically to render the electric valves 111 and 112alternately conductive and non-conductive, their control grids 115 areconnected to their common cathode circuit through current limitingresistances 118 and 119 and opposite halves of the secondary winding 120of a grid drive transformer 121 whose primaryl winding 122 is connectedto any suitable source 123 of alternating current of the desiredfrequency. The electrical midpoint 124 of the secondary winding 120 andthe cathodes 114 are connected to ground.

The master inverter 105 operates in the same manner as the invertersillustrated in Figure l, the commutating capacitor 116 being effectiveto commutate the current from one electric valve 11 or 112 to the otherelectric valve when the other electric valve is rendered conductive bythe alternating potential applied to the control grids 115 of theelectric valves.

The voltage induced in the secondary winding 117 is regulated by meansof a saturable reactor 12.6 whose reactive windings 127 are connectedacross the secondary winding 117 and whose saturating winding 123 issupplied from ya secondary winding 129 of a transformer 130 having apair of rectiers 1.31 and 132 between its end terminals and one side ofthe saturating winding 123. The other side of the saturating winding isconnected to the electrical midpoint 133 of the secondary winding 129.The primary winding 134m of the transformer 13? is connected across thesecondary winding 117.

The amount of direct current tiowing through the saturating winding 128is controlled by a magnetic amplier 134 whose reactive windings 135 and136 are connected in series with the rectitiers 131 and 132. Theimpedance of the reactive windings varies in accordance with the amountof direct current flowing in the control wind ing-125. The controlwinding is supplied with direct current by a full wave rectier 137 whosecathodes 138 and 139 are connected to opposite sides of the secondarywinding 140 of a transformer 141 whose primary Winding 142 is connectedacross the secondary winding 117. One side of the control winding isconnected to the anodes 143 and 144 of the rectiier through a controlelectric discharge means 145 and la glow discharge means 146 as well asthe reactor 147 of a filter 14S which also includes the capacitors 149and 150. The glow discharge means, which acts as a voltage regulator, isconnected in series with a resistance 151 between the -anodes 143 and144 and the electrical midpoint 152 of the secondary winding 140.

The cathode 153 of the control electric discharge means 145 is connectedto the common juncture or connection 154 of the glow discharge means 146so that it is maintained at a substantially constant potentialregardless of the variations in the voltage across the secondary winding117 and therefore across therterminals 102 and 103 of the outputcircuit. The control grid or control member 155 of the control electricdischarge means 145 is -connected through an adjustable contact 156 to aresistance 157 connected between the anodes of the rectifier 137 and theelectrical midpoint 152 of the secondary winding 140 so that thepotential impressed on the control member 155 varies directly inyaccordance with the voltage across the secondary winding 117 andtherefore of the voltage across the terminals 102 and 103 of the outputcircuit.

Assuming now that the master inverter is in operation and applying analternating voltage of predetermined value to the output circuit, thecontrol electric discharge means is transmitting a certain amount ofcurrent to the control winding of the magnetic amplifier and theimpedance of the reactive windings is of such value that the amount ofdirect current transmitted to the saturating winding 128 of thesaturable reactor 126 is maintaining the impedance of the reactivewinding 127 at a value such that the alternating voltage output of themaster inverter is of the desired predetermined value.

If the voltage across the terminal 102 and 103 tends to ride above thepredetermined value, the potential impressed on the control member 155becomes less negative while the potential of the cathode 153 remainssubstantially constant due to the voltage regulating action of the glowdischarge means 146. As a result, the conductivity of the electricdischarge means 145 is increased and more current flows through thecontrol winding 125 of the magnetic ampliiier. The impedance of thereactive windings and 136 of the magnetic amplifier is decreased and theamount of current transmitted to the saturating winding 128 by therectitiers 131 and 132 is increased. This increase in the amount ofcurrent in the saturating windings decreases the impedance of thereactive windings 127 of the saturable reactor and the alternatingvoltage across the output terminals 102 and 103 therefore decreases tothe predetermined value.

Conversely, if the voltage across the terminals 102 and 103 tends tofall below the predetermined value, the potential impressed on thecontrol member 155 becomes more negative while the potential of thecathode remains substantially constant due to the voltage regulatingaction of the glow discharge means 146.r As a result, the conductivityof the control electric discharge means is decreased and less currentiiows through the control winding 125 of the magnetic amplifier. Theirnpedance of the reactive windings 1.35 and 136 of the magneticamplifier is thus increased and the amount of current transmitted tothe. saturating winding 128 by the rectiers 131 and 132 is decreased.This increases the impedance of the reactive windings 127 ofthesaturable reactor and the alternating voitage across the terminals 102and 1133 thereforerises to therpredetermined value. In this manner, the.voltage across the terminals 102 and 103 is maintained constant.

The slave inverters 166 and 107 are substantial dupli- Cates of themaster inverter 105, and therefore, corresponding elements of lsaveinverters and the master inverter have been provided with the samereference numerals, the letter n being added to each reference numeralof each such corresponding element of the slave inverter 1dr? and theletter b being added to each reference numeral of each sucncorresponding element ot' the above inverter 1&7.

rIhe secondary winding 11%; of the slave inverter 106 is connected tothe terminals 1,12 and 1M to energize one phase of the output circuitand the secondary winding 117b of the slr-.ve inverter 107 is connectedto the terminals 1tl3-and 1G4- to energize another phase of the outputcircuit. in order that the phases of the alternating voltages of themaster inverter and the slave inverters be displaced by 120 electricaldegrees, the control members 115er of the eiectric valves 11151 and11211 of the slave inverter 106 are connected to the secondary winding120 of the grid drive transformer through the phaseshiiting circuitswhich include the resistance 158 and capacitor 159'connected in seriesacross the secondary winding 120 and the resistance 160 and capacitance161which are also connected in series across the secondary winding 120.The control member 115:1 of the electric valve 115.: is connected to thecommon connection 162 of the resistance 160 and the capacitor 161 whilethe control member 115e of the electric valve 112a is connected to thecommon connection 163 of the resistance 158 and the capacitor 159.

The control member 115b of the electric valves 111i: and 112!) aresimilarly connected to the secondary winding 120 of the grid drivetransformer through the shifting circuits which include the resistance164 and the capacitance 16S connected in series across the secondarywinding 120 and the resistance 166 and the capacitor 167 which are alsoconnected in series across the secondary winding 120. The control member11511 of the electric valve 11215 is connected to the common connection16S of the resistance 166 and the capacitor 167 while the control member115i: of the electric valve 111b is connected to the common connection169 of the resistance 164iand the capacitance 165.

The alternating potentials impressed on the control members of tl eelectric valves of the three inverters are thus separated in phase bythe phase shifting circuits so that three phase alternating voltageappears across the output terminals 102, 163, and 204.

In order to maintain a proper balance between the alternating currentoutput of the master inverter 105 and the alternating current output ofthe slave inverters 106, a pair of resistances 170 and 171 are connectedin series with the resistance 157:1 of the slave inverter 106 betweenthe anodes 14d-a of the rectiier 137:1 and the electrical midpoint 152eof the secondary winding 140e. A direct current potential of onepolarity which varies in accordance with the alternating current outputof the master inverter is impressed across the resistance 170 by meansof the rectifier 172 whose output terminals 173 and 17d are connected toopposite sides of the resistance 17d and whose input terminals 174g and174b are connected to opposite sides of the secondary Winding 175 of atransformer 176 whose primary winding 177 is connected in series withthe secondary winding 117 of the transformer 108 of the master inverter.The rectiier 172 may include a plurality of selenium rectiers 178connected in the usual way so that the rectier 172 acts as a full waverectier.

A direct current potential of the opposite polarity, which varies inaccordance with the alternating current output of the slave inverter 1%,is impressed across the resistance 171 by means of the rectifier 179whose output terminals 180 and 181 are connected to opposite sides ofthe resistance 171, and whose terminals 132 and l10 183 are connected toopposite sides of the secondary winding 184 of a transformer 185 whoseprimary winding 186 is connected in series with the secondary winding117zz of the transformer 10Sa of the slave inverter 106.

it will be evident now that the potential impressed on the controlmember g of the control electric discharge means 145.1 will vary notonly in accordance with the alternating voltage of the output or" theslave inverter but also with the balance between the alternating currentoutputs of the master inverter and of the slave inverter, since thepotentials applied across the resistances and 171 are of oppositepolarities. For example, if it be assumed that system is in operation,that the inverters are supplying equal predetermined amounts ofalternatcurrent to the output terminals 102, 103, and 10st, thepotentials impressed across the resistances 170 and 171 are of suchvalue that the potential impressed on the control member 15521 maintainsthe conductivity of the electric discharge means 145i: at a certainvalue. If the alternating current output of the slave inverter now tendsto increase above the predetermined while that of the master inverterstays constant, the potential across the resistance 171 also increaseswhile the potential across the resistance 17) remains constant. As aresult, a less negative potential is impressed on the control member155:1, the control electric discharge device 1450i is rendered moreconductive and direct current tlows through the saturating winding 128aof the saturable reactor 126a and the impedance of the reactive windings127a is decreased thus decreasing the alternating current output to thepredetermined value. Conversely, if the alternating current output ofthe slave inverter decreases, the control electric discharge means 14521is rendered less conductive, the amount of direct current in thesaturating winding 123,11 is decreased and the impedance of the reactivewinding 12751 is increased, thus increasing the alternating currentoutput of the slave inverter 106 to the predetermined value. Similarly,if the alternating current output of the master inverter 10S tends tovary from the predetermined value, the conductivity of the controlelectric discharge means 145g will be varied to vary the alternatingcurrent output of the slave inverter 106 in accordance with thevariations of the alternating current output of the master inverter andmaintain the alternating current output of the slave inverter equal tothat of the master inverter. It will be apparent that in this lattercase, the alternating current output of the two inverters will varysimultaneously but in the same degree and in the same direction so thatin all cases the balance or ratio between the alternating current outputof the two inverters will be maintained constant.

It will be apparent that the ratio between the alternating currentoutputs of the master inverter and the slave inverter need not be one toone, but may he set at any predetermined value by proper choice of thenumber otturns in the primary windings 177 and 186. For ei;- ample, ifthe primary winding 177 has twice as many turns as the primary windingwhen the secondary windings 17S and 184 have equal numbers or" turns,the alternating current output or the slave inverter will be twice asgreat as that of the master inverter this one to two current balance orratio will be maintained constant as described above.

The balance or ratio between the alternating current outputs of themaster inverter 105 and the slave inverter 107 is similarly regulated.rrhe resistance 170 and the resistance 187 are connected in series withthe resistance 157b of the slave inverter 107 between the anodes 1Mb ofthe rectier 13711 and the electric midpoint 152i: of the secondarywinding 140b.

A direct current potential of a polarity opposite that impressed acrossthe resistance 170, which varies in accordance with the alternatingcurrent output of the slave inverter 107 is impressed across theresistance 187 byv 11 means of the rectiiier 188 whose output terminals189 and 190 are connected to opposite sides of the resistance 187 andwhose input terminals 191 and 192 are connected to opposite sides of thesecondary winding 193 of a transformer 194 whose primary winding 195 isconnected in series with the secondary winding 117b of the transformer198i) of the slave inverter 107.

It will be apparent that a predetermined ratio or balance between thealternating current output of the master inverter and of the slaveinverter 107 is maintained constant in the same manner as is maintainedconstant the predetermined ratio or balance between the alternatingcurrent outputs of the master inverter and the slave inverter 106.

It will be seen now that an electric translating system has beenprovided for transmitting energy from a direct current supply circuit toa three phase alternating current load circuit which includes a masterinverter 195 and a pair of slave inverters 136 and 107 connected inparallel between the supply and load circuits. It will also be seen thatthe master inverter is provided with a voltage regulating means whichmaintains the voltage of the three phase output circuit substantiallyconstant and that a current balance sensing circuit is provided todetect the balance or ratio between the alternating current outputs ofthe master inverter 195 and of the slave inverters 106 and 107 andprovides constant voltages which are impressed on the control members155a and 155]; of tie control electric discharge means 145er and 145brespectively, to maintain the balance between the alternating currentoutput of the master inverter and the slave inverters substantiallyconstant.

it will be obvious to those skilled in the art that various changes andmodifications may be made in the illustrated and described embodimentsof the invention without departing from the invention and it isintended, therefore, in the appended claims to cover all such changesand modifications which fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. An electric translating system for transmitting energy from a directsupply circuit to an alternating load circuit comprising, a plurality ofinverters connected in parallel between said supply circuit and saidload circuit, each of said inverters having a voltage regulating means,the voltage regulating means of one of said inverters being responsiveto the voltage of said load circuit to maintain constant the voltage ofsaid load circuit; current balance sensing means for detectingvariations in the ratio between the amounts of current transmitted tothe load circuit by one of the said inverters and individually every oneof the remainder of said inverters, said voltage regulating means ofevery one of the remainder of said inverters being controlled by itsassociated current balance sensing means to maintain substantiallyconstant the ratios between the amounts of current transmitted to theload circuit by said one of said inverters and individually every one ofthe remainder of said inverters.

2. An electric translating system for transmitting energy from a directcurrent supply circuit to an alternating current load circuitcomprising, a pair of inverters connected in parallel between saidsupply circuit and said load circuit, each of said inverters having avoltage regulating means, the voltage regulating means of one of saidpair of inverters being responsive to the voltage of said load circuitfor maintaining constant the voltage of said load circuit; a currentbalance sensing means for detecting variations in the ratio between theamounts of current transmitted by said inverters, the voltage regulatingmeans of the other of said pair of inverters being controlled by saidcurrent balance sensing means to vary the voltage of the output of saidother of said pair of inverters in accordance with the ysaid ratio tomaintain said ratio constant.

3. An electric translating system 'for transmitting-energy from a directcurrent supply circuit to an alternating current load system comprising,a pair of inverters connected in parallel between said supply circuitand said load circuit, each of said inverters having a regulating meansresponsive to variations in a control voltage for varying thealternating voltage of the output of the inverters, a voltage sensingmeans connected to the regulating means of one of said inverters and theload circuit for producing a control voltage which varies in accordancewith the voltage of said load circuit for maintaining the voltage ofsaid load circuit constant; and means responsive to the ratio betweenthe amounts of current v transmitted to the load circuit by the pair ofinverters for producing a control voltage which varies in accord-` ancewith said ratio and connected to the voltage regulating means of theother of said inverters for varying the voltage of the output of theother of said inverters in accordance with the variations in said ratioto maintain said ratio constant.

4. An electric translating system for transmitting energy from a directcurrent supply circuit to an -alternating current load circuitcomprising, a pair of inverters connected in parallel between saidsupply circuit and said load circuit, each of said inverters having aregulating means responsive to variations in a control voltage forvarying the alternating voltage of the inverter; a voltage sensing meansconnected to load circuit for producing a lirst control voltage whichvaries in accordance with the voltage of said load circuit, said voltagesensing means also being connected to the voltage regulating means ofone of said inverters whereby said rst control voltage and said voltageregulating means maintain the Voltage of said load circuit constant; anda current balance sensing transformer having a pair of primary windingsand a secondary winding, one of said primary windings being connected tosaid one of said inverters for inducing a voltage of one polarity insaid secondary winding which varies in accordance with the alternatingcurrent output of said one of said inverters, the other of said primarywindings being connected to the other of said inverters for inducing avoltage of opposite polarity in said secondary winding which varies inaccordance with the alternating current output of the other of saidinverters, said secondary winding being connected to the Voltageregulating means of said other of said inverters whereby the voltage ofthe output of said other of said inverters varies as the ratio betweenthe alternating current output of said inverters.

5. An electric translating system for transmitting energy from a directcurrent supply circuit to an alternating current load circuitcomprising, at least three inverters connected in parallel between saidsupply circuit and said load circuit, each of said inverters having aregulating means responsive to variations in a control voltage forvarying the alternating voltage of the output of each of the inverters,a voltage sensing means connected to the load circuit producing a rstcontrol voltage which varies in accordance with the voltage of said loadcircuit, said voltage sensing means also being connected to theregulating means of one of said inverters whereby said rst controlvoltage varies the voltage of the output of said one of said invertersto maintain constant the voltage of said load circuit; and a currentbalance sensing transformer for each of the others of said inverters,each of said current balance sensing transformers having a pair ofprimary windings and a secondary winding, one of said primary windingsof each of said current balance sensing transformers being connected tosaid one of said inverters for inducing a voltage of one polarity insaid secondary winding of each of said current balance sensingtransformers which varies in accordance with the alternating currentoutput of said one of said inverters, the other of said primary windingsof each of said current balance sensing transformers being connected toits associated inverter for inducing a voltage of opposite polarity inthe secondary winding which varies in accordance with the alternatingcurrent output of its associated inverter, the secondary winding of eachof said current balance sensing transformers being connected to theregulating means of its associated inverter whereby the voltage of theoutput of each of said other inverters varies as the ratio between itsalternating current output and the alternating current output of saidone of said inverters.

6. An electric translating system for transmitting energy from a directcurrent supply circuit to an alternating current load circuitcomprising, a plurality of inverters connected in parallel between saidsupply circuit and said load circuit, each of said inverters having avoltage regulating means including a saturable reactor provided with adirect current saturating winding and a control means responsive to acontrol voltage for varying the amount -of direct current flowingthrough the saturating winding; a voltage sensing means connected to theload circuit producing a first control voltage which varies inaccordance with the voltage of said load circuit, said voltage sensingmeans also being connected to the control means of the saturable reactorof one of said inverters whereby said iirst control voltage varies thealternating voltage of the output of said one of said inverters tomaintain constant the voltage of said load circuit; and a currentbalance sensing transformer for every one of the remainder of saidplurality of inverters having a pair of primary windings and a secondarywinding, one of said primary windings of every said current balancesensing transformer being connected to said one of said inverters forinducing a voltage of one polarity in said secondary winding of everysaid current balance sensing transformer which varies in accordance withthe alternating current output of said one of said inverters, the otherof said primary windings of every said current balance sensingtransformer being connected to its associated inverter for inducing avoltage of opposite polarity in the secondary winding which varies inaccordance with the alternating current output of its associatedinverter, the secondary winding of every current balance sensingtransformer being connected to the control means of the saturablereactor of its associated inverter, whereby the voltage of the outputsof every one of said remainder of said plurality of inverters varies asthe ratio between its alternating current output and the alternatingcurrent output of said one of said inverters.

7. An electric translating system for transmitting energy from a directcurrent supply circuit to an alternating current load circuit comprisinga pair of inverters connected in parallel between said supply circuitand said load circuit, each of said inverters having a voltageregulating means including a saturable reactor provided with a directcurrent saturating winding and a control means responsive to a controlvoltage for varying the amount of direct current owing through thesaturating winding; a voltage sensing means connected to the loadcircuit producing a irst control voltage which varies in accordance withthe voltage of said load circuit, said voltage sensing means also beingconnected to the control means of the saturable reactor of one of saidinverters whereby said rst control voltage varies the alternatingvoltage of the output of said one of said inverters to maintain constantthe voltage of said load circuit; and a current balance sensing meansconnected to said inverters for producing a second control voltage whichvaries in accordance with the ratio between the alternating currentoutputs of said inverters, said current balance sensing means also beingconnected to the control means of the other of said inverters wherebysaid second control voltage varies the alternating voltage of the outputof said other of said inverters to maintain constant said ratio betweenthe alternating current output of said inverters.

8. An electric translating system for transmitting energy from a directcurrent circuit to a polyphase alternating current circuit comprising atleast three inverters connected between said circuits, each of saidinverters directly energizing one phase of said polyphase circuit, meansfor maintaining the alternating current outputs of said invertersdiering in phase in a predetermined manner, each of said invertershaving a voltage control means for controlling the voltage of itsalternating current output, the voltage control means of one of saidinverters being responsive to the voltage of said alternating currentload circuit to maintain constant the voltage of said load circuit;current balance sensing means for detecting variations in the ratiosbetween the amounts of current transmitted to the load circuit by saidone of said inverters and each of the other of said inverters, saidvoltage regulating means of each of said other inverters beingcontrolled by its associated current balance sensing means to maintainsubstantially constant the ratios between the amount or currenttransmitted to the load circuit by each of said other inverters.

9. An electric translating system for transmitting energy from a directcurrent supply circuit to three phase alernating current load circuit;three inverters connected in parallel between said circuits, each ofsaid inverters directly energizing one phase of said load circuit, meansfor maintaining the alternating current output of said invertersdiffering in phase by electrical degrees, each of said inverters havinga voltage regulating means responsive to a control voltage; voltagesensing means connected to the voltage regulating means of one of saidinverters and to said load circuit for producing a control voltage whichvaries in accordance with the voltage of said load circuit -formaintaining the voltage of said load circuit constant; pair of currentbalance. sensing means responsive to the ratio between the amount ofcurrent transmitted to the load circuit by said one of said invertersand each of the other of said inverters for producing control voltageswhich vary in accordance with said ratios, and means connecting saidbalance sensing means to each of said other inverters for varying thevoltage of the output of each of said other of said inverters inaccordance with the variation in said ratios to maintain said ratiosconstant.

lO. The device of claim 9 wherein each of current balance sensing meanscomprises a plurality of serially connected resistances; current sensingmeans connected to said one of said inverters for producing a directpotential which varies in accordance with the alternating current outputof said one of said inverters, means connecting said current sensingmeans to one of said resistances for impressing said direct potentialacross one of said resistances, a rcurrent sensing means connected to anassociated inverter of said other inverters for producing a directpotential which varies in accordance with the alternating current outputot" the associated inverter, said direct potentials being or" oppositepolarities whereby resultant potentials are produced which vary inaccordance with the ratios between the alternating current outputs ofsaid one inverter and of said other inverters said voltage regulatingmeans of said other inverter being responsive to said potentials tomaintain substantially constant the ratios between the amount of currenttransmitted to the load circuit by said one of said inverters Iand theamount of current transmitted to the load circuit by each of said otherinverters.

l1. An electric translating system comprising a plurality of invertersconnected in parallel between a direct current supply circuit and analternating current load circuit, each of said inverters having aregulator means responsive to a control voltage for maintaining constantthe output voltage transmitted to said load circuit by each of saidinverters, voltage sensing means connected to said load circuit and theregulator means of one of said inverters for producing a control voltagewhich varies in accordance with the voltare of said load circuit wherebythe voltage of said load is maintained constant with respect to theoutput voltage of said one of said inverters,

Y current balance sensing means connected to said one of ReferencesCited in the le of this patent said inverters and the regulator means ofthe rest of said Y Y UNITED STATES PATENTS inverters for producing acontrol voltage which varies in Y A Y Y accordance with the ratio ofcurrents transmitted to said 21038505 WmogrdV "APL 21: 1936A load bysaid one of said inverters and said rest of said 5 212471785 Puppe July1 1941

